Combustion engines typically emit a much louder exhaust sound when the engine is initially started while the engine is cold. Once the engine is warmed up, the exhaust sound emitted is substantially decreased. A number of factors effect the noise difference including the fact that cold engines are fed a richer fuel mixture during the warm up period.
The exhaust noise reduction properties of the muffler or other engine exhaust silencer are effected by the length and shape of the resonance chambers of the muffler as well as the flow path into and exhausting from the muffler. Conventional mufflers are designed to be static in their muffling capability and produce a fixed amount of noise suppression, due in particular to the fixed length of their resonance chambers and the resulting flowpath through the muffler housing.
As a result, such a muffler when installed on an internal combustion engine may be excessively loud during the “cold start” and warmup condition (when the engine and exhaust system are cold) since the muffler is tuned with the proper or desired loudness and general sound emission characteristics during warm engine operation of the engine and exhaust system. As such, conventional mufflers can cause loud and sometimes obnoxious exhaust sounds during the first several minutes of engine operation after starting the engine.
As a consequence, there is an unmet need for an exhaust system with temperature dependent variable acoustic properties. Such a muffler should be configured to increase noise suppression during the “cold start” conditions of an engine to eliminate the excessive noise. Such a device should thereafter decrease noise suppression once the engine and muffler are warmed to avoid inhibiting engine performance and to provide a desirable sporty exhaust sound to be emitted at a proper sound volume and quality at all times during the long term warm operation period of the engine.
With respect to the above, before explaining at least one preferred embodiment of the engine muffler invention in detail or in general, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangement of the components or the steps set forth in the following description or illustrated in the drawings. The various apparatus and methods of the disclosed muffler invention are capable of other embodiments, and of being practiced and carried out in various ways, all of which will be obvious to those skilled in the art once the information herein is reviewed. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
As a consequence, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing temperature variable mufflers for internal combustion engines and the like, and for carrying out the several purposes of the present disclosed device and method. It is important, therefore, that the embodiments, objects and claims herein, be regarded as including such equivalent construction and methodology insofar as they do not depart from the spirit and scope of the present invention.